The semiconductor photonic device substrate is formed by stacking compound semiconductors with various compositions on a substrate made of, for example, GaAs, SiC or sapphire. The compound semiconductors are generally compounds of group-III elements such as Al, Ga, and In and group-V elements such as N, P and As.
FIG. 1 shows an example of a cross section of a semiconductor photonic device substrate of an LED (Light Emitting Diode). A buffer layer 102, a DBR (Distributed Bragg Reflector) layer 103, an n-clad layer 104, an active layer 105, a p-clad layer 106, and a current diffusion layer 107 are stacked on a substrate 101.
The buffer layer 102 is a layer grown for improving the junction property of crystal with the upper DBR layer 103 at the time of successive crystal growth on the substrate 101. The DBR layer 103 is provided so that the light coming to the substrate side is reflected to the upper side of the LED, and it is made up by stacking two types of films different in composition and refractive index many times. The n-clad layer 104 is an n-type semiconductor for providing a function of a diode. It has also a function of adjusting the direction of light and improving the junction with the active layer 105, and a group-VI element such as Se and Te is doped thereto so as to give an n-type function. Note that the doping of the group-VI element is carried out also to the DBR layer 103 and the buffer layer 102 to improve the electrical properties.
The active layer 105 is made up by stacking two types of extremely thin layers different in composition and electron energy of a conduction band and a valence band (barrier layer and well layer) many times. This forms the MQW (Multiple Quantum Well) and achieves the strong light emission at a specific wavelength (color). The p-clad layer 106 is a p-type semiconductor for providing a function of a diode, and also has the similar function to the n-clad layer 104. The current diffusion layer 107 is provided so as to adjust the current flow and has a large thickness. A group-II element such as Mg is doped into the p-clad layer 106 and the current diffusion layer 107. By applying a voltage to this laminated structure while setting a high electric potential (high potential 111) to an upper side and a low electric potential (low potential 112) to a lower side, the light emission occurs in the active layer 105 and a light 121 is taken out upward.
This semiconductor photonic device substrate is fabricated by the successive crystal growth in one chamber of the MOCVD equipment through a single operation. FIG. 2 shows the structure of the chamber of the MOCVD equipment. The substrate 203 with its front surface directed downward (opposing plate 207 side) is held by a susceptor 201. Several to several tens of substrates 203 can be arranged on the susceptor 201. A soaking plate 202 for preventing the temperature nonuniformity is disposed on the back surface side of the substrate 203. In order to equalize the growth rate in the plane of the substrate 203, the susceptor 201 and the substrate 203 are individually rotated at the time of the crystal growth. The temperature is controlled by a heater 206 so as to promote the crystal growth on the surface of the substrate 203, and the several types of source gas 204 are introduced in the chamber while controlling the flow rate. By this means, crystals with specific compositions are grown.
The source gas 204 includes TMG (Trimethyl Gallium: (CH3)3—Ga), TMA (Trimethyl Aluminum) and TMI (Trimethyl Indium) for introducing the group-III element, NH3, PH3 and AsH3 for introducing the group-V element, and H2Se and Cp2Mg (Cyclopentadienyl Magnesium) as a dopant material. In addition, carrier gas for obtaining a predetermined flow rate is also used.
For example, Japanese Patent Application Laid-Open Publication No. 2007-246341 (Patent Document 1) shows an example of a manufacturing method of an LED semiconductor photonic device substrate. As an example of the crystal growth by the metal organic vapor phase epitaxy (MOVPE) method, the fifth embodiment of Patent Document 1 discloses the method in which an n-type contact layer, an electro-static protection layer, a doped semiconductor layer 1, a doped semiconductor layer 2, a doped semiconductor layer 3, an n-clad layer, an MQW active layer, a p-clad layer and a p-type contact layer are successively crystal-grown on a substrate while controlling growth conditions such as temperature, source gas and its flow rate. In each of the layers, a plurality of layers are crystal-grown while adjusting conditions more finely. Also, it includes the descriptions about the crystal growth of predetermined thicknesses for all of the layers, and therefore, the growth time has to be set as a growth condition. Fourteen types of layer compositions are provided in total. Note that, since the MQW has a repetitive multi-layer structure, the detailed number of layers reaches several tens of layers.
In the mass production of the semiconductor photonic device substrate, the process is repeated in a manner such that a set of substrates including several to ten and several substrates is processed at once and then a next set of substrates is processed. When repeating the process several tens of times, reactants are attached inside the chamber, so that the quality of the fabricated photonic device substrates does not satisfy the control standard. Therefore, maintenance such as the cleaning of the inside of the chamber and the part replacement is carried out. After the maintenance, the chamber state changes due to the individual variability of the members that make up the chamber and the variation in setting and cleaning, and therefore, the growth conditions have to be checked in order to obtain the predetermined composition and film thickness. More specifically, the check of the composition by the photoluminescence emission and the growth rate preinspection for obtaining the growth time of each layer are carried out.
In the semiconductor photonic device substrate, crystal growth of a large number of layers is successively performed, and since the multiple layers are provided and they have significantly different thicknesses, it is difficult to measure the thickness of the semiconductor photonic device substrate in a non-destructive manner. Therefore, crystal growth is carried out individually for only a predetermined time by using an individual substrate for each composition and the film thickness is measured, thereby obtaining the growth rate. Accordingly, the growth rate preinspection has to be carried out several tens of times in each maintenance.
Further, Japanese Patent Application Laid-Open Publication No. 2000-53494 (Patent Document 2) shows that the film stack is deposited at once and the thickness of each layer is obtained by one measurement (X-ray reflectometry), thereby obtaining the growth rate. In this measurement method, however, the X-ray reflectometry apparatus is required, and the number of types of the stacked films (two types of GaAs and AlGaAs in the embodiment) and the film thickness (20 to 40 nm in the embodiment) are assumed to have a physical limit due to the interference in the reflectometry. Due to these problems, the method of Patent Document 2 is not suitable for the film thickness measurement of the multiple-material/multiple-layer stacked films having different thicknesses.
The semiconductor wafer of an LSI product also becomes a product by stacking multi-layer films. For example, Japanese Patent Application Laid-Open Publication No. 2008-117887 (Patent Document 3) describes a film stack structure using a low-k material as an insulating film. A manufacturing method of a semiconductor device in which two types of oxide films are stacked as insulating films and copper (Cu) is embedded through photolithography and etching is shown. Although the LSI semiconductor wafer is fabricated by repeating this manufacturing method several to ten and several times, the film formation, photolithography and etching are carried out by respectively different equipments. Further, the two types of oxide films are formed by the coating method and the CVD method, respectively, and are formed by different equipments. Therefore, the preinspection of the film-formation rate is carried out for each layer (in each equipment), and the film-formation rate is not estimated by using the preinspection results of the other layer and other equipment. Deposition of an oxide film made of TEOS material and film deposition of a gate structure such as polysilicon, WSi (tungsten silicon) and SiN (silicon nitride) are also carried out in addition to the low-k material, but the process of successively forming the films of the multilayer structure like that of the compound semiconductor photonic device substrate is not carried out.